Telephone conference arrangement



Patented Aug. 26, 1930 UNITED STATES PATENT oFFicE GEORGE CBISSON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TOAMEBICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK TELEPHONE CONFERENCE ARRANGEMENT Application filed March 2,

This invention relates to improved arrangements for giving conference telephone service between two or more groups of peo ple.

In the arrangements of the invention there .Will be provided at each station for a group a loud speaker by which-the group may hear speech delivered before any other group. The grou however, will listen to its own speakers ire'ctly. This will presentcertain advantages over an arrangement for simply interconnecting two public address systems as it will not be necessary to bypass speech from the nearby transmitter into the loud speaker and will eliminate the cli'ects of talkv er echoes so that the minimum line transmission loss will be limited only by listener echoes. Each station for a group will also be provided with a transmitter so that its speakers may be heard by the other group without requiring any speaker to talk close to the transmitter. Echoes due to acoustic coupling between the loud speaker and the transmitter will be eliminated by echo suppressor circuits. Other features and advantages of the invention will appear more fully from the detailed description thereof hereinafter given.

The invention may be more fully understood from the following description together with the accompanying drawing in the Figures 1. 2 and 3 of which the invention is illustrated. Fig. 1 is a circuit diagram illustrating a preferred embodiment of the in,- vention. In Figs. 2 and 3 are circuit diagrams illustrating modified forms of the invention. Similar reference characters have been utilized to denote like parts in all of the figures.

In the arrangements of Fig. 1 is shown a section of a transmission line L to which might be connected a number of stations for groups desiring conference telephone service. Each station would comprise a receiving circuit 2 including a loud speaker 3 and a transmitter circuit 4 including a transmitter 5. The receiving circuit 2 and the transmitter circuit 4 would be connected to line. L by means ofthe hybrid coil 1 and balancing network N so that they will be approximately 1928. Serial No. 258,596.

in conjugate relationship. Included in the receiving circuit 2 would be an amplifier 10, and included in the transmitter circuit 4 would be the amplifiers 8 and 9. The loud speaker 3 will be required to deliver a volume of sound to the conferees substantially equal to that due to their own speech. The transmitter will be exposed to sound from the loud speaker 33, and hence it will be necessary to use echo suppressing devices to prevent echoes and distortion due to acoustic coupling. even if this coupling is not close enough to cause singing. echo suppressor devices (3 and 7 are provided. One of these will be connected to each local circuit, and in response to voice currents transmitted-thereover, will close a short circuit across the. other local circuit to disable it. \Vhere it is possible to so locate and adjust the transmitter and loud speaker that singing will not occur, the arrangements of Fig. 1 will suppress the echoes. The hybrid coil 1 is utilized to give the transmitting echo suppressor 7 the greatest possible operating margin over the receiving echo su pressor 6 when speech begins to act on t e transmitter. It is pointed out that if repeatercd circuits are used to connect the diflerent conference groups, it is preferable to arrange the echo suppressor contacts so that the short circuits (or opens) will not be applied directly to the terminals of the hy- Accordingly, the

brid coil in order not to disturb the impedance presented toward the line L and so produce echoes.

If the acoustic coupling. between the loud speaker and the transmitter is such that singmg is encountered. the arrangements illustrated in Figs. 2 and might be utilized. The arrangements of Fig. 2 are substantially similar to those of Fig. 1 except that an extra set of contacts are provided to normally close a short circuit 12 across the transmitter circuit 4. A delay network 11 is also provided in circuit 4 between short circuit 12 and the input terminals of the echo suppressor 7'. With these arrangementsthe speech which actuates transmitter 5 will be held up by the delay network until the device 7 operates to open short circuit 12 and to close a short circuit across the receiver circuit 2. Obviously, singing could not occur because of the normally closed short circuit 12 across the talking circuit 4.

1n the arrangements of Fig. 3, the relativel v slow transmission of sound through the air is utilized to secure the delay provided for in Fig. 2 by the delay network 11. The echo suppressor 7 is connected by a separate cirruit 14 to a suppression transmitter 15 which will be located closer to the conference group than the pickup transmitter 5. Accordingly, when one of the conferees speaks, the echo suppressor 7 is operated by the suppressor transmitter 15, and the necessary circuit changes made by the time the sound reaches the pick-up transmitter 5.

It is pointed out that with the arrangements of the invention, the transmitter branch 4 is made normally inoperative by means of the sing suppressing contacts of the short circuit 12 closed across said circuit. The advantage in this will be seen from the fact that if the transmitter branches of all stations are normally operative, the room noises from all the stations involved are impressed upon the line at all times when speech 1s not being transmitted; hence, the resulting relative level of total noise in the line will be higher than the relative noise level in the noisicst conference room. Furthermore, by making the transmitter branch 4 normally inoperative, the receiving echo suppressor 6 is required to discriminate only against line noise as room noise will only be on during the time someone is talking, and will be only that due to one room. The receiving echo suppressor can then be made quite sensitive so that the transmitting echo suppressor will be protected against false operation by strong echoes due to acoustic coupling. A further advantage of the arrangements of the invention consists in the fact that due to the lack of talker echoes, the arrangements of the invention are suitable for operation over any two-way or multi-way transmission network which will give substantially equal transmission losses over the different paths and satisfactory quality for loud speaker operation.

While the arrangements of the invention have been disclosed as embodied in certain specific arrangements which are deemed desirable, it is pointed out that they are capable of embodiment in other forms without departing from the spirit of the invention as defined by the appended claims. a

What is claimed is:

1. In association with a transmission line, an arrangement of telephone circuits and apparatus adapted for use as a unit in a conference system, comprising a receiving path, a loud speaking receiver therein, a normally disabled transmitting path, a transmitter therein exposed to sound from said receiver, said receiving path and said transmitting abling the opposite path in response to voice waves.

2. In association with a transmission line, an arrangement of telephone circuits and apparatus adapted for use as a unit in a conference system, comprising a receiving path, a loud speaking receiver therein, a normally disabled transmitting path, a transmitter therein exposed to sound from said receiver, said receiving path and said transmitting path being connected substantially conjugately to the transmission line, means for dis abling either of said paths in response to voice waves in the other path, means in the transmitting path for clearing said ath in response to voice waves therein, an means for insuring the operation of said clearing means before the arrival of the actuating voice waves at the point at which the transmitting path is normally disabled.

In testimony whereof, I have signed my name to this specification this 29th day of February, 1928.

GEORGE CRISSON. 

